In order to more efficiently utilize the power grid electric energy, a switch power supply technology has begun to be widely applied in power factor correction techniques. In the prior art, it is common practice to insert a power factor correction (PFC) circuit between the diode rectifier bridge and the load of the circuit so that the current drawn from the AC power supply also is a sine wave signal, and its phase follows changes in supply voltage. After the addition of the power factor correction circuit the power factor value may be close to 1.
A PFC circuit implementation as shown in FIG. 1, is applied to a boost converter (BOOST CONVERTER). The converter comprises an inductor L, a switch device S, a freewheeling diode D, an output capacitor Cout, and an integrated PFC circuit. The supply voltage Vac passes through the diode rectifier bridge as an input for boost converter. The boost converter converts the input voltage to obtain the output voltage Vout. The PFC circuit comprises an error amplifier U1, an multiplier U2, a comparator U3, a RS flip-flop U4, a driving module U5 and a zero current detection circuit (ZCD) U6. The PFC circuit samples the output voltage Vout and inputs it to the error amplifier U1. One input of the multiplier U2 is the output error feedback signal Verror of the error amplifier U1 and the other input is the divided signal Vin of the supply voltage Vac so that the output current waveform becomes a sine wave following the power supply voltage waveform. The sampling resistor R1 and the external switching device S are connected in series to obtain a switching current signal. When the voltage across the sampling resistor R1 is higher than the output of the multiplier U2, the comparator U3 and the RS flip-flop U4 are turned over and the external switching device S is turned off by the driving module U5. When the zero current detection circuit U6 detects that the inductor current drops to 0, the external switching device S is turned on. Through the above control mode, the critical conduction mode control is realized, and the realization is in a simple way, and especially suitable for the configuration of power factor correction circuit with small and medium power.
However, there are still some problems should be improved in the current technology, such as the accuracy of the output current.